﻿1903] CURRENT LITERATURE 293 



ness are not, as usually held, due to an effort on the part of the plant to reach 

 the light. It is shown that the stimulating action of light maybe transmitted 

 through a considerable interval of both space and time, even affecting organs 

 subsequently formed, so that conclusions drawn from so-called "partial etio- 

 lation'* have frequently been erroneous. Often there is a direct action of 

 darkness in producing morphological changes. It is well proven that in all 

 cases a great difference exists in the morphological differentiation of tissues 

 developed in darkness and in light, and in this discussion the distinction 

 between growth and development is kept clearly in view. The author con- 

 cludes that '' none of the phenomena of etiolation or of diminished growth in 

 light may be ascribed to the direct influence of light upon the tissues or cells 

 concerned, but rather upon the organism as a whole/' 



It is, however, impossible to give in a brief review any adequate idea of 

 the author's views upon the various aspects of the subject. He himself has 

 tacitly admitted the futility of such an attempt by not providing a summary 

 for the reader. 



There can be no question of the great value of this contribution by Dr. 

 MacDougal to a most important part of plant physiology. The vast array 

 of carefully planned observations forms a substantial contribution in itself and 

 the discussion brings the subject into a new and clearer light. An ample 

 index both to the literature cited and to the text and illustrations completes 

 the volume. — J. C. Arthur. 



The heaths of northern Germany. 



The fifth volume of Vegetation der Erde differs from those that have 

 preceded in that a single formation is dealt with, rather than a country or a 

 natural phytogeographic subdivision. Graebner"^ has made the north German 

 heaths a special study for a number of years, and in 1895 he published an 

 extensive treatise on the subject, wherein many of his present results were 

 anticipated. The close relationship between heaths and moors is clearly 

 shown, and the impossibility of using the water content of the soil as the chief 

 distribution factor is well brought out. Graebner makes a strong plea (as ho 

 has done in former papers) for a chemical classification of soils and plant for- 

 mations. Adopting this idea, the heath belongs to the soil group which is poor 

 m certain food materials, particularly potash, lime, and phosphoric acid. For 

 chemical reasons, he believes that a heath soil can never develop a natural 

 forest. The author's concept of the heath is rather broad, including not only 

 areas dominated by ericaceous shrubs, but open tracts in which there is neither 

 ^ good tree growth nor a close grass turf; ligneous plants dominate, espe- 

 cially low shrubs. What we call pine or oak barrens would probably be 

 included in Graebner's heath. Moors or peatbogs also are difficult to delimit 

 irom the heath, many species, indeed, being common to both. 



'Graebner, P., Die Heide Norddeutschlands uiid die sich anschliessenden For- 

 niationen in biologischer Betrachtung. 8vo, pp. xii + 320. With map. Leipzig: 

 Wilhelm Engelmann. 1901. Price ^21.50. 



